1. Field of the Invention
The present invention relates to a rotary compressor and, more particularly, to a rotary compressor having an oil groove provided in the journal portion of the crankshaft thereof.
2. Description of the Prior Art
First of all, a conventional rotary compressor (hereinafter referred to simply as "compressor") will be described hereinunder with reference to FIG. 1 which is a vertical sectional view of a known rotary compressor. The conventional rotary compressor has a curved oil feeding pipe 9 which is immersed in an oil 10 stored in the lower part of a casing 1. The oil feeding pipe 9 is provided therein with a coiled spring 8 which rotates with a crankshaft 7. The oil is transferred to the end portion of the crankshaft 7 on the side thereof which is closer to the coiled spring 8 through the leads of the coiled spring 8. The oil then passes through oil grooves 7A, 7B and 7C which are respectively formed in the outer peripheries of a sub-journal 7S, a crank pin 7b and a main journal 7M of the crankshaft 7 thereby to lubricate these slide portions. The compressor of this type, however, suffers the following disadvantages: The oil grooves 7A and 7C respectively provided on the sub-journal 7S and the main journal 7M of the crankshaft 7 need to be formed such as to spiral in the direction opposite to a rotational direction 13 of the crankshaft 7 as shown in FIGS. 1 and 2 in order that the oil is forcedly transferred from the end portion of the subjournal 7S of the crankshaft 7 to the main journal 7M thereof aided by the pitch angle between the oil grooves 7A and 7C. For this reason, as shown in FIG. 3, it is not possible to provide the oil groove 7A on the subjournal 7S such that the oil groove 7A is not located in a portion of the sub-journal 7S which is heavily subjected to a load 16 applied to the crankshaft 7 as a reaction force to a force on the crankshaft due to the fluid pressure in the cylinder during the operation of the compressor. Consequently, the area for receiving a maximum load is reduced by an amount corresponding to the area of the oil groove 7A which fact causes the surface pressure at the oil groove 7A on the sub-journal 7S to be greatly increased, so that the sub-journal 7S may cause seizure or other failure. Thus, there is a strong possibility of deterioration in the compressor's reliability. Further, the gap at the slide portion of a roller 11 is sealed by the oil which is supplied thereto after being heated at the sub-journal 7S. In other words, the gap is sealed by the oil which is lowered in viscosity and, therefore, sealing properties are impaired, resulting disadvantageously in a reduction in volumetric efficiency of the compressor.
It is to be noted that the reference numerals 4, 5 and 6 in FIG. 1 respectively denote a spring, a vane and a cylinder.
FIG. 4 is a vertical sectional view of a conventional known compressor of the type wherein oil grooves 3A and 12A are respectively formed in the inner peripheries of a main bearing 3 and a sub-bearing 12. By the pumping action of the vane 5 vertically moving, the oil is sucked in from a small bore 14a opened in a portion of an oil feeding pipe 14 immersed in the oil 10. The oil is passed through the oil feeding pipe 14 and is supplied into an oil feeding hole 7d defined by the inner periphery of the crankshaft 7 from the end portion of the sub-journal 7S on the side thereof which is closer to the oil feeding pipe 14. Then, the oil is fed to the sub-journal 7S, the crank pin 7b and the main journal 7M through oil holes 7e, 7f and 7g which provide communication between the oil feeding hole 7d and the outer peripheries of the sub-journal 7S, the crank pin 7b and the main journal 7M, thereby to lubricate the slide portions while passing through the oil grooves 3A and 12A respectively provided on the inner peripheries of the main bearing 3 and the sub-bearing 12. This type of oil feeding mechanism, however, cannot effect the forced oil feeding by means of the oil grooves 3A and 12A, since they are fixed. Moreover, since there are changes in the amount of oil fed to the oil holes 7e, 7f and 7g, particularly when the amount of oil fed by the pumping action is small, imbalance is disadvantageously easily produced between the supplies of oil to the main bearing 3 and the sub-bearing 12.